The present invention relates to a measuring method for a measuring positional relation between a measuring device and various types of sensors in a system, which is used to acquire 3D (three-dimensional) space information of a mobile object such as a vehicle, based on detection data from the various types of sensors. The invention also relates to a measuring device for carrying out the measuring method.
In an on-board type 3D (three-dimensional) space information acquiring system to be installed on board of a mobile object such as a vehicle, information such as position, speed and attitude of the vehicle from a position measuring device and from the various types of sensors are combined, and these information need to be outputted as the 3D space information at a present position of the vehicle.
As a system for acquiring the positional information, a GPS (Global Positioning System) is known, and as a device for detecting position, speed and attitude of a mobile object, an IMU (Inertial Measurement Unit) and the like are known. By the GPS, coordinate position on a ground surface can be measured based on a signal from an artificial satellite. By the IMU, the present position, the attitude, etc. of a vehicle can be determined based on a moving direction, a speed and an attitude of the vehicle.
The GPS can acquire accurate positional information. However, it is not possible to acquire the positional information by the GPS at a place where a radio wave does not reach, for example, at a place where the radio wave is interrupted by construction such as building or at a place such as a valley, a tunnel, etc. where the radio wave does not reach.
On the other hand, the IMU can output detection signals on moving direction, moving speed, acceleration and attitude of a moving object at high density. Base on these detection signals, relative amount of changes within short time can be outputted with very high accuracy. Therefore, when the IMU is used, the information on the present position of the object can be acquired by calculating a relative position from the position acquired by the GPS even when a receiving the radio wave by the GPS is interrupted. However, errors of the positional information acquired are accumulated by drifting of sensor as time elapses.
Therefore, both of the positional information of the GPS and the positional information as acquired from the IMU based on calculation of relative position are acquired. Under a condition where the positional information of the GPS cannot be acquired, the positional information from the IMU is calculated as a relative position to the positional information of the GPS, and the present position of the vehicle is determined. Under a condition where the positional information is acquired from both of the GPS and the IMU, weighting is performed on the information, which corresponds to the situation where the positional information has been acquired, and an accurate position of the vehicle is determined.
For the purpose of carrying out the measurement of the position of the vehicle by combining the positional information from the GPS, the signals from the IMU and information from other sensors, a position, which can act as a measurement standard in various types of sensors in a measuring coordinate system, must be determined accurately.
Normally, carriers and other means, which are commercially marketed, are used when the GPS and the IMU are installed on board of a vehicle. As a result, the positions of installation of the GPS and the IMU are indefinite. In this respect, it is necessary to accurately measure positional relations (offset amount) between the measurement standard of the GPS and sensors installed at each site of the vehicle and between the measurement standard of the IMU and the sensors.
In the past, as a method to accurately determine the offset amount, a method to use a measuring device such as a total station has been known. The total station itself is a system with high cost. Also, a certain high level of skill and technique is required to perform the measurement by using the total station. Further, to use the measured values as the offset amount, the processing such as coordinate transformation is needed, and this means that it is necessary to use programs for calculation.
In this respect, if a measuring device such as a total station is not available, accurate measurement cannot be performed. Even when it may be available, complicated working procedures are required.